1. Field of the Invention
A narrow wall waveguide slot array is an antenna system that uses slotted waveguides to radiate energy. This invention is an improvement in the field of slotted waveguides.
2. Description of the Prior Art
Conventional slotted waveguides have utilized "inclined" rectangular slots in the narrow wall of a waveguide to radiate electromagnetic energy. The longer edges of the slot were not orthogonal to the axis of the waveguide, but were inclined from right angles to a greater or lesser degree. The inclined edges of the slot distorted the RF current in the wall containing the slot, and caused an electric field across the slot. The electric field induced across the slot radiated energy into space.
Inclined waveguide slots can cause a serious problem: they radiate a large amount of cross-polarized radiation. This cross-polarization does not contribute to main beam gain and is totally lost in radiated lobes in other directions. Systems utilizing inclined-slot waveguide arrays can be undesirable because the cross-polarized lobes contribute to ground clutter and increase vulnerability to radiation-sensitive missiles.
Cross-polarization suppressing baffles have been used to suppress the undesirable lobes caused by inclined slots. However, such baffles introduce considerable weight and cost in large arrays.
Another prior art approach has been to utilize "non-inclined" slots with waveguide irises located inside the waveguide and adjacent to each slot. Non-inclined slots normally do not radiate energy, but the pressure of an iris adjacent to the slot induces an electric field across the non-inclined slot, resulting in a controlled amount of radiation. This solution, however, has suffered from two problems. The cost of installing the irises has been prohibitive for large arrays of slots. Further, the capacitive portion of the iris must be relatively deep to obtain a sufficiently large excitation for efficient arrays. But the deep capacitive portion of the iris reduces the high power handling capability of an array due to arcing from the iris edges.
Therefore, a major problem in this field has been the elimination of undesirable cross-polarized lobes without simultaneously increasing significantly the weight or cost of the system.